capephysics labs2 v4

BISHOP ANSTEY HIGH SCHOOL EAST AND TRINITY COLLEGE EAST (BATCE) Sixth Form TRINCITY, TRINIDAD AND TOBAGO, WEST INDIES

CENTRE NO. 160570

CXC CAPE Physics Unit 2 Lab Manual 2015-2016

c  Copyright by Bishop Anstey High School East and Trinity College East  (BATCE) 2015 All Rights Reserved

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Rules and Regulations of the Laboratory 1. All experime experiments nts in this this labora laborator tory y manual manual must be perform performed ed and writte written n scripts scripts for each experiment must be submitted to your class teacher to obtain a practical coursework mark. 2. Commencement of sessions: You You are expected to be at your experiment station station punctually. 3. Preparation: Preparation: Laboratory Laboratory manuals manuals are available available at the class website. website. These manuals manuals contain a description of all the laboratory experiments that must be performed as part of the requirements requirements for CAPE Physics SBAs. SBAs. Students Students are required required to prepare adequately for their assigned laboratory experiment prior the start of the session. Preparation includes reading the experimental description adequately and performing the necessary research to enable one to perform the experiment with ease in the laboratory. 4. Starting Starting experiments: experiments: All laboratory laboratory equipment equipment must be checked checked prior to students students commencing commencing their experiments experiments.. DO NOT switch ON equipment equipment until it is checked by your teacher!! teacher!! 5. Laboratory Laboratory report submission: submission: All laboratory laboratory reports must be submitted submitted to the class teacher teacher ONLY ONLY on the date it is due. If your laboratory report submission submission date falls on a public holiday, then the report must be submitted on the next available school day. Laboratory reports must be submitted with the appropriate cover sheet (with all the details completed) completed) and a signed anti-plagia anti-plagiarism rism sheet. Students Students will given until the following following day, of performing performing the experiment, experiment, at 10:30am 10:30am (break time) to submit submit their lab reports. At this time the student would sign the teachers’ lab record book as evidence the lab was submitted. 6. Absenteeism Absenteeism:: Students Students absent from any experiment must provide provide a medical/e medical/excuse xcuse to administration. 7. Students Students who are absent on the day of the lab practical practical activity activity would would be scheduled with the lab technician to perform the lab within a one week period from the date of  iii

the missed lab. lab. They are to sign the lab technician’ technician’ss rcord book with the date the lab was performed. performed. This report would be due the following following day at 10:30am. 10:30am. 8. Students Students who fail to submit their lab reports reports at the deadline deadline would be marked as no work submitted. submitted. Special Special allowance allowancess would would be given given to studetns studetns with a valid valid excuse, for example a death in the family or physical injury. This excuse must be confirmed via a note and phone call from the parents or medical where applicable, on the day the report is due. 9. Laboratory Laboratory requirements: requirements: For each laboratory laboratory session students are required to bring their laboratory manual, writing paper, graph pages, a scientific calculator and other stationery items inclusive of pen/pencils, erasers, rulers and geometrical instruments (if needed for the laboratory experiment). 10. Laboratory Laboratory attire: attire: Students Students are required to wear a laboratory laboratory coat and closed shoes while present in the laboratory. 11. Work stations: stations: Students Students must remain at their assigned assigned work station for the duration of the laboratory laboratory session. If a student student needs to leave the work station, station, permission permission must be sought and granted from the class teacher. 12. Difficulties with with an experiment: Students experiencing difficulties with experiments experiments should seek assistance from their class teacher. 13. At the end of each laboratory laboratory session: At the end of each experiment, experiment, students students are requir required ed to take take all their their results results to their their teache teacherr for review review and correct correction ion.. These These results pages must be signed by the teacher and must be included in the laboratory report. The signed results pages must not be altered after the teacher has fixed his/her signature. Students must seek the permission of the teacher prior to the exiting of the laboratory laboratory at the end of each session. session. Additionall Additionally y, before students students leave leave their work  station they must ensure that they have removed all their personal belongings and replac replaced ed all equipme equipment nt to the designat designated ed area. area. A check check of equipm equipment ent assigned assigned to each student will be made by the technicians at the end of each laboratory exercise. Students should not leave the laboratory until this check is made. Students will have to pay a compensation compensation fee for missing or broken equipment. equipment. 14. Copying Copying and plagiarism plagiarism in the lab scripts are strictly strictly forbidden. forbidden. Plagiarized Plagiarized work  work  will not be marked. 15. General General rules: Students Students are not permitted to eat, drink or smoke in the laboratory. laboratory. The use of the internet is strictly permitted for laboratory research only. 16. Mobile Mobile phones: phones: The use of mobile mobile phones phones is not permitt permitted ed for the duration duration of the laboratory session unless approval is given. iv

Policy Principles Practical work and lab reports are an important part of the student’s understanding of the subject area. They provide an avenue where theory taught in the classroom can be tested, applied applied and/or proved. proved. Practical Practical work engages engages students, students, helps them to develop develop important important skills, to understand the process of scientific investigation and develop their understanding of concepts. Lab Reports form 20% of the student’s Caribbean Advanced Proficiency Examinations (CAPE) Physics grade. Timely submission of work ensures students can receive timely feedback from their teache teachers. rs. Also Also scripts scripts written written up during during the practical practical activit activity y ensures ensures that the students students recall information information clearly clearly about the experimental experimental procedure procedure (e.g. the method, sources of  error, teacher’s guidelines).

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Format for Written Reports 0. Cover Sheet Title of Experiment, your name, date that experiment was performed, partners’ names. (First and last names. Get the spelling right!)

1. Title Titles Titles should be straightforward straightforward,, informati informative, ve, and less than ten words (i.e. Not "Lab #4" but "Lab #4: Sample Analysis using the Debye-Sherrer Method").

2. Aim/Objective(s) 3. Theory/ Introduction 1-2 paragraphs. paragraphs. Summarize Summarize the basic physics of your experiment. experiment. Include Include equations and other principle things the reader would need to know in order to understand the experiment. Keep it short! If there are standard standard or accepted accepted values known these should be included in this section.

4. Apparatus This can usually be a simple list, but make sure it is accurate and complete.

5. Diagram These should be clearly labelled with a title.

6. Method/ Procedure/ Experimental Details This section describes describes the process in chronologica chronologicall order. Using clear paragraph structure structure (or step by step format), explain all steps in the order they actually happened, not as they vi

were were suppose supposed d to happen. happen. If you’ve you’ve done it right, right, another another researc researcher her should should be able to duplicate your experiment. It is always written in past tense.

7. Precautions & Sources of Error Indicate what steps were taken to reduce/eliminate random and systematic errors. Note: Mistakes are not classified classified as errors.

8. Results The original raw data that you take in the lab. This should be easy to follow, in tabular form. Poor data recording skills lead to poor writeups. If your raw data is illegible, the grade will suffer. The table should have a title and include the uncertainty of the measurement as well as the unit in the heading (e.g. Variable  ±  uncertainty in the measurement/ unit).

9. Sample Calculations Calculations Include a few of your calculations in this section, e.g. one of each type. Do not show each and every calculation.

10. General Analysis The computed results are shown in a clear and concise manner utilizing properly labelled tables and graphs. “Table/ “Table/Graph Graph showing showing results” is not an appropriate appropriate title. Each column of the table table must have a heading heading and units, units, if applicab applicable. le. Tables ables must be bordere bordered d by 4 lines lines and neatly neatly construct constructed. ed. If a graph graph is to be drawn, drawn, it must include include the follo followin wing: g: title, title, appropriate appropriate scales, accurate accurate plotting of points, points, drawing drawing best straight straight line (smooth (smooth lines through experiment experimental al data points) and labeling labeling of axes. Slope calculation calculationss should be included after the graph. Each graph should convey convey a complete message message and be fully understandable without referring to any other section in the report.

11. Error Analysis This section must include the pertinent computed uncertainties (error estimates). It is important here that the rule governing significant figures be used in computing and displaying these values. vii

12. Discussion This is the most important important part of your report, because here, you show that you understand understand the experiment beyond the simple level of completing it.   Explain. Explain. Analyse. Analyse. Interpret. Interpret. Some people like to think of this as the "subjective" part of the report. By that, they mean this is what is not readily observable. This part of the lab focuses on a question of understanding "What is the significance or meaning of the results?" To answer this question, use both aspects of discussion: results indicate indicate clearly? clearly? What have have you found? Explain Explain what Analysis: Analysis: What do the results you know with certainty based on your results and draw conclusions. Interpretation: Interpretation: What is the significance of the results? What ambiguities exist? What questions might we raise? Find logical explanations for problems in the data. The experimental experimental results should be compared with predicted values. values. If known values exist, exist, the results should should be compared compared with these and a reference reference given (see below). below). Discrepancies should be considered in the light of the experimental error obtained and other random and systematic errors not evaluat evaluated ed numerically numerically in ‘Results’. If no known known value value is availabl available, e, it is still important important to consider consider all the possible errors. Then discuss the experiment in general, its advantages and failings, procedural difficulties, ways of improving it etc. If any questions questions are asked in the lab manual, manual, they should be answered answered in this section of  the report.

13. Final Results with Errors and Conclusion Conclusion This should indicate how well the experiments have fulfilled the aims stated at the beginning. ning. Simply Simply state state what you know now for sure, sure, as a result result of the lab, lab, and justify justify your statement.

14. References Any source of material used in the report should be listed here.

Note: Labs are always to follow this format except for planning and design labs. Labs are to be communicated in a logical way using correct grammar and spelling.

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Contents

Rules and Regulations of the Laboratory

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Policy Principles

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Format for Written Reports

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1

Lab #1: Electr Electrosta ostatic ticss

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Lab #2 - ORR: ORR: Capaci Capacitanc tancee

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Lab #3 - ORR: ORR: Capac Capacito itorr Disc Dischar harge ge

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Lab #4 - ORR ORR & MM: MM: EMF EMF and Intern Internal al Resi Resistan stance ce

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Lab #5 #5 - ORR: ORR: Determin Determining ing the the resistanc resistancee of a voltmeter voltmeter

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Lab #6 #6 - A&I: A&I: Resista Resistance nce per per unit unit lengt length h of wire wire D

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Lab #7 - P&D: P.D. P.D. and and I relation relationship ship across across a filamen filamentt

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x

 

CONTENTS 

Chapter 1 Lab #1: Electrostatics A leaf electrometer consists of an aluminum leaf which hangs at an angle when a potential difference  V  XY   is applied betweeen the metal cap case Y  of the electrometer.

Figure 1.1: Leaf Electrometer 1

θ  to

X  and

the vertical

the conducting

CHAPTER 1. LAB #1: ELECTROSTA ELECTROSTATICS 

2

It is calibrated by connecting different values of  V  XY    across

XY ,

with the following

results: V  XY  /V  ◦ θ 

/

  10 100 11

200 14

300 18

400 23

500 30

600 37

700 45

800 53

900 62

1000 69

1100 74

1200 78

Table 1.1: a)  Plot a graph of  θ   θ  against V  XY  . b)  The rate of change of  θ   θ  with V  XY   is known as the sensitivity of the electrometer. Over what range of potential differences is the sensitivity approximately constant? Calculate the sensitivity over this range. Show all your working. c)  It is suggested that, between 300 V  and 700 V , the potential difference is proportional to sin θ .

Draw up a suitable table of values and plot a graph to test this suggestion. Does your graph support the suggestion?

Chapter 2 Lab #2 - ORR: Capacitance To determine a capacitance by measuring the time constant of RC circuits In this experiment you are to determine a capacitance by measuring the time constant of  RC circuits. Record all observations observations and deductions deductions in your lab book. a)  Connect the circuit shown in Figure 2.1 using a 10

k Ω  resistor

both switches are open.

Figure 2.1: RC Circuit Circuit 3

for R. Make sure that

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CHAPTER 2. LAB #2 - ORR: CAPACIT CAPACITANCE 

Close switch A switch  A and  and wait for the voltmeter reading to reach

V 0 , its

maximum maximum value. Record

V 0  and the value of  S   S , where  S  =  = 0.632 V 0 .

Open A Open  A and  and close B close  B to  to discharge the capacitor. b)  The time constant τ  of the circuit is equal to the time taken for the voltage to reach

S 

after switch A  is closed with the capacitor initially discharged and switch B  open. Measure the time constant of the circuit as accurately as you can. c)  Replace the 10 k Ω resistor with one of the other resistors and determine the new value for τ . Repeat the procedure procedure until you have values values of the time constant constant for circuits containing each of the resistors provided. Tabulate all your values of  τ  and R and  R,, the value of the resistance used.  /s (y-axis) against R against R /   / k  k Ω(x-axis). d)  Use a graph page and plot a graph of  τ   τ  /s Given that  τ  =  RC , use the graph to obtain a value for C, the capacitance of  C.  C. resistance values are quoted to a tolerance of 1%. State a range of values in which e) The resistance the true value of capacitance might lie. Show how you arrived at your answer.

Chapter 3 Lab #3 - ORR: Capacitor Discharge To inve invest stig igat atee th thee rate rate at whic which h a capa capaci cito torr disc discha harg rges es th thrrough ough a voltmeter voltmeter Part 1 Connect ect the the circu circuit it show shown n in Fig. Fig. 3.1.  3.1. You shou should ld ensur ensuree that that the the post postiive (+) (+) term termin inal al (a)(i)   Conn of the power supply is connected to the + terminal of the capacitor C 1 (blue). Initially switch  S  should be closed.

Figure 3.1: Capacitor Circuit 5

CHAPTER CHAPTER 3. LAB #3 - ORR: CAPAC CAPACITO ITOR R DISCHARGE  DISCHARGE 

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(b )

(ii)

Record the inital reading V o  of the analogue voltmeter.

(i)

Open switch switch S and simultaneously start a stopwatch.

(ii)

Measure and record values of the potential difference difference V  and time  t  until the reading on the voltmeter becomes less than V o /10.

( c)

(i)

Plot a graph of V  (y-axis) against  t  (x-axis).

(ii)

Use your your graph graph to determine determine the the time time  τ  for the potential difference across the capacitor to fall from V o  to V o /5.

(d )

(i)

 are related by the formula τ  and C  are τ  =  = CRv ln 5

where  R v  is the resistance of the voltmeter and   is C  is

the capacitance of the capacitor C 1 .

Use your answer from (c) from (c) (ii) and (ii)  and the value of the capacitance C (written on the capacitor) to determine a value for  R v . (ii)

Justify the number of significant significant figures which which you have given given for R v .

Part 2 (e )

(i)

Connect a second capacitor C 2  (yellow) in series with the first capacitor C 1  (blue) so that the circuit is now as shown in Fig. 3.2

Figure 3.2: Capacitor Series Circuit

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Repeat (b)(i) and  and (b)(ii) (ii)   Repeat (b)(i)  (b)(ii).. (f )

(i)

For the second second set of results results and using the the same set of axes axes as before, plot a graph of  V  against  t .

(ii)

Use the graph to determine determine a value value for the capacitance capacitance of the capacitor capacitor C 2 .

Chapter 4 Lab #4 - ORR & MM: EMF and Internal Resistance Apparatus Dry cell, digital ammeter  ( 0 − 0.20 A)  whose resistance is known, decade resistance box, switch, connecting wires, metal film resistors  (1.1k Ω, 2 .2k Ω, 3 .3k Ω, 5 .5k Ω, 10 .0k Ω, 12 .0k Ω, 15 .0k Ω,  18 .0k Ω).

Figure 4.1: Circuit Circuit

Method Connect up the circuit as shown in the diagram, figure 4.1 figure 4.1.. • Connect

•  Take 100 Ω out of the resistance box and, if the current is measurable on the ammeter 8

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scale record both the current and the resistance box reading.

•  Gradually reduce the resistance of the box until the current has risen to about 0.1 A. Tabulate the results: Resistance box reading  R  (Ω)

Ammeter reading

1/ I  (  ( A−1 )

 I  (  ( A)

Table 4.1:

• Plot a graph with values values of  R  R /Ω as ordinates (y-axis) against the corresponding value of   I 1 ( A−1 ) as abscissae (x-axis).

Experimental Details 1. The current through through most resistance resistance boxes should never never exceed exceed about 0.1 A. 2. Before Before taking taking any readings readings give give all the plugs in the resistan resistance ce box a half-t half-turn urn to ensure that they are properly properly in. 3. If the resistance box possesses an infinity plug it may be used instead of a circuit key key. 4. Check Check the ammete ammeterr for zero error and if necessary necessary re-set re-set for zero reading reading by the adjusting screw provided.

Theory and calculation calculation Let

 represent E  represent

the e.m.f. of the cell, RC  its internal resistance, supposed constant,

R  the

resistance box reading,  R A  the resistance resistance of the ammeter ammeter and  I  the current in the circuit. Then  E   R + RC  + R A

=  I 

 

(4.1)

CHAPTER CHAPTER 4. LAB #4 - ORR & MM: EMF AND INTERNA INTERNAL L RESIST RESISTANCE 

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Therefore,

 ·  R =  E  ·



1  I 



− ( RC  + R A )

 

(4.2)

1 −1 Hence, the graph of  R  R /Ω (ordinates) against  I  ( A ) (abscissae) is a straight line whose

slope is the magnitude of  E   E  and whose negative intercept on the  R  axis is the magnitude of 

( RC  + R A ). Measure the slope from the co-ordinates of two convenient points on the straight line. Produce the line to cut the axis of  R   and read off the intercept intercept.. Subtra Subtract ct the ammeter ammeter resistance to find the internal resistance  RC  of the cell.

Errors and accuracy The error in

R  may

be neglected in comparison with the much larger possible error in

I 

which depends on the range, sensitivity and scale markings of the ammeter used. From the graph estimate the likely errors in  E  and  RC  from the difference difference between between the values values found from the chosen line and those obtained from other possible straight lines drawn through the points (see the handout on Errors, Uncertainties & their Analysis).

Chapter 5 Lab #5 - ORR: Determining the resistance of a voltmeter Apparatus Analogue Voltmeter reading to 1.5 or 3V, two accumulators, 4 batteries with battery holder, resistance box of total resistance not less than 1000 Ω, switch, leads with alligator clips, metal film resistors  (1k Ω,  1 .5k Ω, 2 .2k Ω, 3 .3k Ω, 4 .7k Ω,  5 .5k Ω,  8 k Ω,  9 .4k Ω).

Figure 5.1: Circuit

Method • Connect Connect up the circuit circuit as shown in the diagram, figure 5.1 figure 5.1.. 11

12CHAP CHAPTE TER R 5.

LAB LAB #5 - ORR: ORR: DETE DETERM RMIN ININ ING G THE THE RESI RESIST STAN ANCE CE OF A VOLTM OLTMET ETER ER

•  Take out a large resistance from the resistance box is obtained obtained on the voltmeter voltmeter scale. Decrease Decrease

R  and

R  until

note whether any reading

the voltmeter reading is at its

maximum maximum on the scale. Record the resistance R  and the voltmeter reading V .

•   Increase

R  in

suitab suitable le steps to make make full full use of the voltmet voltmeter er scale. scale. Tabula abulate te the

results:

Resistance box reading  R  (Ω)

Voltmeter reading V  (V )

1/V  (V −1 )

Table 5.1:

• Plot a graph with values of  R  R /Ω as ordinates (y-axis) against the corresponding value 1 of  V  (V −1 ) as abscissae (x-axis).

Experimental Details 1. The current through through most resistance resistance boxes should should never exceed exceed about 0.1 A. 2. Before Before taking taking any reading readingss give give all the plugs plugs in the resista resistance nce box a half-tu half-turn rn to ensure that they are properly properly in. 3. If the resistance resistance box possesses an infinity plug plug it may be used instead instead of a circuit circuit key. key. 4. Check Check the ammete ammeterr for zero error and if necessary necessary re-set re-set for zero reading reading by the adjusting screw provided.

Theory and calculation calculation Let  E  represent represent the total e.m.f. of the circuit,  R  the resistance box reading, V  the voltmeter reading, and  RV  the resistance of the voltmeter.

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Then the current  I  in the circuit is  I  =  =

E 

(5.1)

 R + RV 

assuming the resistance of the accumulators in the circuit to be negligible. Hence, the voltage across the voltmeter is V  =  I RV 

=

E   R + RV 

· RV 

 

(5.2)

Rearranging,  R + RV 

=  E RV  ·

1

(5.3)

V 

or  R =  E RV  ·

Thus, the graph of  R  R /Ω (ordinates) against

1 V  1 V 

− RV 

 

(5.4)

(V −1 ) (abscissae) is a straight line whose

negative intercept on the  R  axis is the magnitude of  R  RV  .

Errors and accuracy The error in

R  may

be neglected in comparison with the much larger possible error in  V 

which depends depends on the range, sensitivity sensitivity and scale markings of the voltmeter voltmeter used. From the graph estimate the likely errors in

RV    from

the difference between the values found

from the chosen line and those obtained from other possible straight lines drawn through the points (see the handout on Errors, Uncertainties & their Analysis).

Chapter 6 Lab #6 - A&I: Resistance per unit length of wire D Apparatus 1.5V dry cell, analogue ammeter, connecting wires with alligator clips, switch, meter rule, 100cm length of wire (wire B), and 15cm length of wire (wire D).

Figure 6.1: Circuit Circuit

In this experiment you will use a wire (labelled B (labelled  B)) of known resistance per unit length (which should be taken to be 4.00 Ωm−1 ) to find the combined resistance of a cell and an ammeter ammeter.. You will use this value to find the resistance resistance per unit length length of a second wire (labelled D (labelled  D). ). 14

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Procedure (a) Set up the circuit circuit of figure 6.1 figure  6.1.. wire  B in  in the circuit, record the following quantities in a table (b)  For different lengths of wire B S 

the scale scale reading reading of the the current as shown shown on the the ammeter ammeter,,

b

the length length of wire B wire B used,  used,

 Rb

the resista resistance nce of length length b of wire wire B  B,, and

1/S  wire  D between  between the switch and the cell. Repeat the procedure procedure of  (c)  Insert 15.0 cm of wire D part (b), record your readings in your table. (d)  Both graphs are of the form  1

 Rb  =  k 

S 

− r 

 

(6.1)

where  k  is   is a constant, and  r  is   is the resistance of the other components of the circuit used.

•  Plot graphs of your values from (b) and (c). For your graphs, use the same axes and scales, extending the  R /Ω axis to include  R /Ω = −2. values for (e) Deduce from the graphs values (i)  the combined resistance of the cell and ammeter, calculate the resistance resistance per (ii)  the resistance of the length of wire  D  used in (c). Hence calculate unit length of wire D wire  D.. (You may assume that the circuit leads have negligible resistance.)

Chapter 7 Lab #7 - P&D: P.D. and I relationship across a filament Objective In this experiment you will investigate the relationship between the potential difference across a filament and the current in it.

Instructions Choosing from the apparatus provided, set up a circuit to enable you to investigate the relationship n

V  ∝  I 

where V  = the p.d. across the filament lamp, lamp,  I  =  =  the

and

current in the filament

n  is a constant, the value of which you are to determine.

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(7.1)